A conventional way to increase the signal to noise ratio of a signal in the frequency domain is to average power realizations of the signal in each frequency bin. For example, a signal in the time domain is sampled, and these time samples transformed in an N point fast Fourier transform into a plurality of frequency bins having N points each. Each of the N points in each frequency bin is then averaged, which typically increases the signal to noise ratio in each bin because noise data sums less coherently than signal data. This can be formulated as: ##EQU2## where a is average signal in the particular frequency bin, x.sub.i is the ith point, or realization, of the frequency bin, i=1, 2, . . . , N. However, this approach often proves insufficient in noise environments in which the desired signal is relatively small and steady, but is buried in noise signals which have relatively large temporal amplitude fluctuations. An example of this would be tonals from an underwater acoustic source. Interactions at the surface, such as from weather or from ships on the surface, or impulsive noise such as encountered in the arctic, produce large amplitude, short lived, noise which can bury such underwater signals. These noise signals can be so large that conventional means of detecting the underwater signals, such as the power averaging above, frequently prove ineffective. A similar situation is created by a signal jammer, which outputs intermittent large amplitude signals in order to overwhelm smaller, more constant, signals of interest. Application Ser. No. 07/772,275 by the same inventor, discloses the following improvement over the above straightforward average: ##EQU3## Because the sum depends on 1/x.sub.i, rather than x.sub.i, a' disproportionately attenuates large signals, and thus will improve the signal to noise ratio of relatively small underwater acoustic signals. Although an improvement over straightforward averaging, even more sensitive filters would be useful. Moreover, not all noise environments require the same amount of filtering to produce useful results. It would also be helpful to permit control filter sensitivity by adjusting filter parameters.